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Development of a Speeding-Related Crash Typology

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PRIOR STUDIES

While numerous research studies have explored the effects of speed on crash frequency and severity as well as on the effect of treatments aimed at managing speed (e.g., Transportation Research Board Special Report 254), a previous National Highway Traffic Safety Administration study of particular interest examined an SR crash typology.^(3,4) This study used data from the Crash Avoidance Research Data (CARDfile), the Indiana Tri–Level Study, and FARS to examine the scope of the speeding problem and the characteristics of crashes that are SR.^(5,6,1) CARDfile includes crash data from six States.⁽⁵⁾ In this study, the 1986 CARDfile data were used and included 1.4 million crashes involving about 2.4 million vehicles and drivers.

Based on CARDfile, speed was a factor in about 12 percent of all crashes.⁽⁵⁾ Data from the Indiana Tri–Level Study indicated that excessive speed was a factor in 7.1–16.9 percent of crashes.^(5,6) However, most of the analyses focused on the 1989 FARS data.⁽¹⁾ The key findings included the following:

• Almost 70 percent of all drivers involved in SR fatal crashes were involved in single–vehicle crashes.

• Approximately 36 percent of all fatal crashes on rural roads were SR, whereas only 30 percent of fatal crashes on urban roads were SR.

• SR crashes accounted for only 27 percent of all fatal crashes on straight roadway sections, but they constituted 54 percent of all fatal crashes occurring on curves.

• While only 27 percent of all daytime fatal crashes were SR, 39 percent of nighttime fatal crashes involved speeding.

• About 25 percent of all male drivers involved in fatal crashes were speeding, while only 16 percent of female drivers involved in fatal crashes were speeding.

• Safety belt usage (lap belt and shoulder belt) for drivers involved in SR fatal crashes was found to be only 19 percent. This compares to the usage rate of 37 percent for drivers involved in non–SR fatal crashes.

• Approximately 41 percent of all drivers under the influence of alcohol who were involved in a fatal crash were speeding.

• More than 45 percent of all motorcycle drivers involved in fatal crashes were speeding.

In a second typology–related study, Hendricks, et al. examined data from a sample of 723 relatively severe crashes involving 1,284 drivers collected as part of the National Automotive Sampling System Crashworthiness Data System (NASS CDS) program.^(7,8) Based on in–depth field investigations of the crashes and driver interviews, researchers determined the specific driver behaviors and unsafe driving acts (UDAs) that led to the crashes and the situational driver and vehicle characteristics associated with these behaviors. Each driver's actions were examined to determine whether and how they contributed to the crash, and a ranked list of the most commonly occurring UDAs (e.g., inattention, alcohol impairment, perceptual errors, etc.) was produced. Crash types and driver and behavioral characteristics associated with these higher ranked UDAs were then identified. In situations in which cause could be assessed, excessive vehicle speed was the second leading causal factor, with inattention being the first. Excessive speed constituted exceeding the speed limit; however, it sometimes also included traveling at inappropriate speeds for prevailing weather or roadway conditions (i.e., too fast for conditions). Excessive speed was the primary cause of crashes for 6.8 percent of the drivers who contributed to causation; it was also a primary cause in combination with other causes for an additional 3.8 percent of the contributing drivers and was a contributory cause for an additional 8.1 percent of the drivers. When crash types were examined for the drivers who were excessively speeding, researchers found that speeding was the leading cause of single–driver right– or left–roadside departure with traction loss (i.e., part of run–off–road crashes) and the third leading cause of head–on crashes. Researchers then examined the characteristics of the drivers and roadways in these excessive–speed roadway departure crashes. They found that the more important characteristics of these crashes included that they occurred primarily on curves or on local or collector roadways at night or during clear weather, and the drivers were younger males (less than 35 years old). Males younger than 20 years old comprised 46.2 percent of the sample. Enhanced law enforcement countermeasures were suggested for these crashes.

In summary, two prior studies have developed crash typologies that reference speeding. Both examine data from in–depth crash investigations as part or all of the methodology as well as factors and unsafe driving actions in addition to speeding. This current study is designed to add further information to the findings of those two studies by examining large national databases which include recent crashes as well as by using different methodologies and concentrating solely on SR crashes.

FHWA-HRT-10-024